Electric induction motors are widely used in appliances and machines of all kinds. In particular, induction motors find widespread usage in refrigeration equipment and air conditioners, both for domestic and commerical use. Induction motors may operate from single phase, or three phase, electric power. In the case of common single-phase power, induction motors have many design variations, most notably including:
split phase start, induction run, PA0 capacitor start, induction run, PA0 permanent split capacitor run (PSC), PA0 capacitor start, split capacitor run, PA0 shaded pole induction run; and, PA0 induction/repulsion.
Induction motors operate efficiently only when driving a rated load: e.g., when operating under full load. When a modern induction motor of usual design drives a partial load, considerable inefficiency occurs and, as a result, a lot of energy is wasted. The electrical ENERGY LOSS manifests itself as undue heating of the motor; most common electric motors get very hot (with rated temperature rises of 40 or 50 degrees Centigrade above ambient being commonplace) after a period of operation, even with no load coupled to their output shaft. It is not uncommon for an ordinary major-appliance motor, such as found in a washing machine or the like, to consume several hundred watts even when completely unloaded.
A fundamental concern of my invention is to acheive considerable ENERGY CONSERVATION, which can result in less abuse of our environment and reduced consumption of our non-renewable fuel resources (such as oil gas, and coal) which are commonly used to generate electricity. With operational and regulatory set-backs having been encountered by the electric power industry relative with the construction and use of nuclear power plants, together with severe environmental and economic restrictions on the construction of hydroelectric and other such kinds of power generating plants, there is little near-term expectation that new electric power generating stations will be run from anything other than conventional fuels such as coal, oil, and natural gas. It therefore behooves the electric power industry to try to spread out the consumption of such relatively limited and non-renewable fuels over as long of period of time as possible to allow for the long-term development of some kinds of suitable alternative methods for producing goodly amounts of electric power. The electric power industry is, however, geared mainly to respond to demand and therefore if demand increases they simply must put more generating capacity on-line and as a result of such immediate consideration they also must ignore any issues of how such short-term increases in consumption may impact future power availability and cost. Aside from merely conserving these finite sources of fuel from wasteful consumption, is that of concern for perhaps irreversible contamination of the Earth's atmosphere. The result of such contamination, which in part results from smoke emitted by fossil-fuel power plants, is that of a "greenhouse effect" that tends to increase the Earth's mean temperature, and the detrimental effects of "acid rain" which abounds over much of the United States. Conservation of our fuel resources and protection of our life-supporting environment is the responsibility of every level of society, but certain levels (such as the engineering of manufactured products) carry greater intrinsic responsibility for reducing energy waste than others.
Electrical inefficiency of products is a particular kind of energy waste which is neither the direct responsibility of the electric power producer or the user (consumer) of such products. Under most circumstances, a consumer will purchase a more energy efficient product if that product is not disproportionately priced relatively with a less efficient product. It is therefore important to realize that, with the exception of dedicated energy conservation advocates or zealots, a product having better electrical efficiency will not normally sell well unless it is priced at about the same level as that of less well engineered products having inferior electrical efficiency. My invention therefore endeavors to particularly address the need for reducing energy consumption by mass-marketed products having known high levels of energy waste through techniques and approaches which do not contribute any significant additional cost to the product nor require re-tooling investment by the manufacturer of such products. As a result, any new product based on my invention maintains its price attractiveness to the buyer, while some sales advantage may be leveraged out of the improved efficiency (and resulting savings this means to the customer in his electric bill) by the manufacturer's selling agents. Indirectly, important conservation of our energy resources occurs. However, this latter aspect may be transparent to the usual consumer and, as a result of not being directly meaningful, generally ignored when the user is contemplating the purchase of a new energy consuming product.
Electrical loss and the resulting ENERGY LOSS in the ordinary kind of electric motor mostly takes the form of eddy-current loss in the stator core material, and "copper" or winding-resistance loss. So-called "advances" in insulating materials and magnetic (field) core materials have further aggravated these losses in that, while improved efficiency might be obtainable under FULL-load operating conditions, the percentage of losses tend to soar as the load coupled to the motor is lessened. Reality suggests that most of these kinds of "advances" are aimed at making a "cheaper" motor, and not necessarily a motor having better overall electrical performance in the sense of being able to reduce unnecessary energy consumption. One can quickly realize that the design choice of operating a stator core near saturation, as is allowed in modern motor design, leads to considerable eddy current loss and that this loss remains substantial even when the motor is unloaded. Running a motor's winding very hot, because the plastic insulation used in the motor's construction is more tolerant than ever before, also leads to increased winding resistance and naturally to greater electrical losses. Another consideration is that of (reactive) power-factor decreases brought forth under partial (or no-load) conditions, which causes high apparent current flow through the windings and therefore, even under reduced load, the copper losses remain high. Yet a further consideration of such high magnetic-field operation of a common electric motor is that of the production of relatively high noise levels (e.g., "hum", "buzz", and the like) which are at best annoying. Such noise is related to the same factors which bring about eddy-current losses: noisy operation is in part the result of magnetostriction in the field core material.
A common induction motor, which might be typified by the General Electric type 5KH22EJ0367 that is nameplate rated for 1/3 horsepower, draws about 5 amperes from the 115 volt a.c. line when fully loaded and operating around 3,450 R.P.M. with about 70-80% power factor or better. Even under NO-load, the same motor continues to draw about 3.8 amperes, although the motor current phase very considerably lags the voltage phase and the power factor has slipped to about 0.2-0.3 (i.e., 20-30 percent). It is under this latter NO-load condition (or under a state of partially reduced load) where considerable real electric power is wasted because the actual efficiency of the motor is measurably very poor. To a large extent, this low operating efficiency is caused by the aforementioned eddy-current and copper losses. I have found that taking this same type of motor and, through the expedient of merely reducing the applied line voltage to about 85 volts or so, I can reduce the NO-load current draw to only be about 1.1 amperes. Meanwhile, the operating power factor also increases (because the motor "appears" to be working harder in proportion to the available applied a.c. power). What I have accomplished through this reduction of applied voltage is to bring about a reduction of the magnetic field strength in the stator which results in greatly lowered eddy-current loss, together with reducing the apparent current flow through the field winding which, of course, means a lot less copper loss.
I realize that the singular act of merely reducing the motor's available operating voltage is inappropriate because, while the motor may run satisfactorily with NO-load, it will stall and overheat when the load increases. It also may not start, particularly when operating under load. Therefore it is known to be necessary to alter the magnetic field which is induced by the RUN winding to match the motor's instant loading.
Frank Nola of N.A.S.A., in his U.S. Pat. Nos. 4,052,648 and 4,266,177, describes a controller which varies the power applied to the main stator (running) winding of an induction motor and as such he attempts to reduce magnetic field strength and winding current when the motor is less than fully loaded. Unfortunately, Frank Nola's approach serves to phase-control the power applied to the whole stator (run) winding and as such tends to introduce severe harmonic distortion into the a.c. current waveform which results in parasitic losses which can outweigh any gains which might otherwise be obtained in the motor's net operating efficiency. In effect, Nola introduces loss producing effects which outweigh any gains he might otherwise obtain in the more efficient operation of a common appliance-grade induction motor. Such shortcoming of the Nola device occurs because power flow is drawn only over a portion of each a.c. power half-cycle, after the phase-delayed thyristor is fired. The result is that a.c. power draw causes large changes in the instantaneous a.c. current flow present in the a.c. power cycle after thyristor conduction occurs relative with the negligible level immediately prior to thyristor conduction. The a.c. power cycle distortion introduced by these large and sudden changes in load current draw also tend to become more exaggerated through reactive a.c. line impedances which (albeit mostly resistive) can be quite substantial. The surges caused by phase-delayed power control of such large amounts of current will also cause flicker in any ordinary lights hooked to the same circuits, as is commonplace in domestic wiring practice. As a result of these kinds of parasitic losses and other side effects, phased-delayed firing of a thyristor as the control for total current flow to a motor's run windings is less than satisfactory in most induction motor applications, and as such does not find much commercial useage.
What I have now discovered as a novel and viable alternative to controlling the full power applied to the motor's windings is to instead provide the motor with some plurality of functionally paralleled sets of run windings. For example, two run winding sets may be used, and each set may have somewhat different winding construction (viz, number of turns and wire guage). The result is a main run winding and a supplementary run winding. The main run winding is suitable sized such that, when fully coupled with the a.c. line power, it may provide enough magnetic field strength in the stator to operate the motor under the condition of: a) intermediate loading: b) least expected load: or c) perhaps under a state of no load. The supplementary run winding is then sized to induce sufficient additional magnetic field, when coupled fully with the a.c. line, so that the induced additional field strength may be added to the magnetic field produced by the main run winding, with the combined field having sufficient total strength to operate the motor under full load.
This brings about two modes of operation for the motor: full load capability, and reduced load capability. Under the full load arrangement, the motor will exhibit operating conditions which are equivalent to those of any other ordinary electric motor having but one heavy run winding. Under the reduced or no load condition (when only the main run winding is excited), the motor will continue to operate with a relatively high power factor, good electrical efficiency, and with negligible temperature rise. I find that the novel control of the amount of a.c. power coupled with the supplementary run winding alone may now be accomplished using phase-controlled thyristor power control to adjust the instant stator field strength to the motor's load requirements.
The result is improved overall motor operating efficiency and better energy utilization. Unlike Nola and other prior teachings, the full connection of the main run winding with the a.c. power line under all load conditions serves to snub-out most of the a.c. power harmonic distortion losses because the main run winding draws operating current (under relatively high power factor) over the full a.c. power cycle, whereas the supplementary winding draws only a smallish portion of the a.c. power over each remaining a.c. power half-cycle subsequent to thyristor turn-on. The net result is continued high efficiency for a motor utilizing my invention under varying load conditions.
In most major appliances such as typified by a washing machine, the load demand on the motor changes during different portions of the machine's operating cycle. For example, during wash-agitation the power demand is quite different from that needed during the period when the water in the tub is being pumped out. In the common kind of washing machine, such operating cycle portions are controlled by a programmer such as an electromechanical timer switch or, more modernly, by a microprocessor or other electronic control device. In a similar way, the several portions of the usual operating cycle for dishwashers, clothe dryers and other appliances can vary over a relatively wide range. A Delco (General Motors Corp.) type C-1660 motor, rated for 1/3 horsepower at 1,725 R.P.M. is known to draw about 6.9 amperes under full load, and such a motor has been widely used in Kenmore (Sears and Roebuck Co.) automatic washing machines. Assuming an 80% power factor (under full load) and a true horsepower equalling about 746 watts, such a motor runs about 39% efficient: EQU ((746W/3)/((115V.times.6.9A).times.0.8PF)).times.100=39.173%
As the load is reduced however, apparent motor current remains high: dropping off to about 4.9 amperes under no-load, albeit the power factor is down to about 20-30%. Thus even under such an unloaded condition, the motor still burns about 113 to 170 watts: EQU (115V.times.4.9A).times.0.25PF=140.875W
and additionally, the high apparent current flow (4.9 amperes) continues to cause current-flow losses in the motor winding resistance and in the interconnecting wiring (house wiring, etc.) supplying power to the motor.
I have now found that these earlier kinds of appliance designs can be made considerably more efficient through the expedient of using my novel multi-winding motor and variously modulating the instantaneous amount of electric power fed to the supplementary run winding to best match each of the several portions of each operating cycle while the main run winding is fed full a.c. line power. I have also found that the programmer can be used to fractionally predetermine the amount of a.c. power fed to the supplementary run winding during each machine cycle portion through the expedient of varying the gate turn-on phase delay for a thyristor which serves to feed a.c. power to the supplementary run winding.
In particular, I have found that through the use of two (or more) run windings, with each RUN winding differently proportioned, and with each run winding fed power through a separately controlled (timer cam-actuated) switch contact set, a switchable range of motor excitation levels may be obtained. The novelty I introduce through this operational approach lends itself to use with time-proven electromechanical timer programmers wherein each portion of the appliance's usual operating cycle actuates different switch contact sets to obtain different interaction between the run windings that results in best power utilization for each program cycle step. When my invention is utilized in this manner, no electronic devices such as thyristors and the like are used. Therefore the reliability of the overall appliance product is unchanged, if not made better due to less heat buildup.
In refrigeration systems, and more particularly in air-conditioning systems, the a.c. power needed to operate the compressor may be expected to vary in accord with cooling demand operating conditions or outside ambient temperature influences. It is through the sensing of these operating conditions or influences and their utilization to control the delay for the firing of a control thyristor used to feed a.c. power to a supplementary run winding that considerable savings in electric power can be realized. Like the aforementioned appliance, a central programmer or control circuit may be utilized to produce signals that can vary the time-delay for thyristor turn-on to obtain such supplementary run winding excitation power modulation. The result is a very considerable savings of electrical energy.
I also know that the development of the modern electric motor, as it has evolved over the years, has resulted in considerable investment by manufacturers in equipment for the efficient manufacture of these motors. Furthermore, the user of these motors (particularly the appliance product manufacturer) have developed a level of confidence in the reliability of certain motor design configurations. It is therefore fundamental that you realize that my invention is capable of being incorporated into these earlier motor design embodiments with a minimum of modification with the result that historical reliability and time proven performance is not compromised. Furthermore, manufacturing cost is not affected to any significant extent, because the only change in motor structure is merely that of adding a few more turns of smaller guage wire: the end result is that about the same amount of "copper" winding material is used.
In-so-far as is known to me, no prior induction motor apparatus has brought together the use of a plurality of run windings where one main winding is ordinarily fully excited from the a.c. line over the full power cycle, while the other supplementary winding is switched ON and OFF, or modulated to bring about the most effectual level of motor field excitation necessary to obtain sufficient motor power to meet the instant motor load demand. More particularly, no prior art is known to me in which much of the motor's operating power is drawn over the full a.c. power cycle by the main RUN winding, whilst additional power is drawn over a portion of the cycle by the supplementary run winding with the result that the power drawn over the full cycle by the main run winding serves to be of sufficient magnitude to swamp out and thus minimize waveform distortions and other undesirable influences on operating efficiency which might otherwise be introduced by the phase controlled firing of a thyristor to variously excite the supplementary run winding.
Knowing the advantage of controlling the a.c. power fed to the supplementary run winding under different load conditions, it now follows that in many applications the load requirements may be expected to conform to predictable patterns and therefore the programmer intrinsic with the machine's control apparatus may best constitute a predetermined source of signals suitable for variously modulating the a.c. power fed to the supplementary run winding. The actual amount of a.c. power fed to the supplementary run winding during any given portion of the machine's operating cycle may of course be efficiently controlled by a phase controlled thyristor switch having several different predeterminable values of phase-delayed turn-on period characteristics.
Additionally, I have anticipated that two or more supplementary run windings may be provided, wherein each one is controlled separately to afford several differing levels of field excitation. With two supplementary windings, the following four levels of field excitation can be obtained merely by switching the different windings full-on or full-off.
______________________________________ MAIN SUPPLEMENTARY Motor Power RUN RUN WINDING Operating Mode Winding No. 1 No. 2 ______________________________________ FULL Power FULL ON FULL ON FULL ON PARTIAL Power A FULL ON FULL ON FULL OFF PARTIAL Power B FULL ON FULL OFF FULL ON LOW Power FULL ON FULL OFF FULL OFF ______________________________________
Since operation in this manner may be obtained from purely electromechanical cam-driven timer switches or the like, typified by that of the Part No. 367929 cam operated programmer made by Controls Company of America, my invention's implementation becomes not only uncostly to implement but also unchanges the time-proven reliability of an appliance product which commonly uses such kinds of electromechanical timers. Such "full-on" and "full off" operation of the supplementary run windings (i.e., with power flow over the full a.c. power cycle) by mechanical switch contacts also clearly precludes any detrimental loss effects which might occur from thyristor control of the power levels. Furthermore, it is anticipated that the main winding may be turned off and operation obtained from the excitation provided by the supplementary run winding(s) alone.